


Void-Initiated Encounters, starring Y/N and Gaster!

by Anon_gi



Category: Undertale (Video Game)
Genre: Established Relationship, F/M, Gaster can be such a grumpy pants when he wants to, M/M, Multi, Oh hey look reader can pole dance, Travelling Through Au's, UL Grillby is such a bro, Welcome to Confusion Wonderland people, adding tags as I go, albeit a little awkward but then gets swept up in the music, but not a heavy drinker either, reader is a little salty at the fact that they would lose to gaster in drinking, reader is not a light weight, sudden pov changes from time to time, trying to not mention gender and be as neutral as possible-, yes reader is a little troublemaker
Language: English
Status: In-Progress
Published: 2021-03-04
Updated: 2021-03-13
Packaged: 2021-03-17 08:08:31
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 4
Words: 4,172
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29838579
Author URL: https://archiveofourown.org/users/Anon_gi/pseuds/Anon_gi
Summary: A collection of short stories of Y/N (you) and Gaster falling into the void and ending up in different universes, and meeting Y/N's alternate selves! Hilarity, Awkwardness, and Chaos ensues as Y/N (you) and Gaster realize that many of Y/N's AU's were dating someone else other than Gaster!
Relationships: Papyrus (Undertale)/Reader, Sans (Undertale)/Reader, W. D. Gaster/Reader
Comments: 3
Kudos: 27





	1. This could've went in worse ways -Gaster

**Author's Note:**

> Fair warning, this story doesn't have a schedule. What does that imply? It's going to update at random intervals. From days to weeks to months!
> 
> Read with caution

**Notes for the Chapter:**

> ooo, prologues, yay~ (sarcasm)

Y/N and Gaster were going on their monthly ‘date’ across the multiverse. This time, Y/N was picking a place. Their solution? Jump into the void and let it transport them somewhere random. Y/N, somehow someway, befriended the void and now you could call them… best friends? I think that’s the right wording.

And so that’s what they did, much to the protest of W.D Gaster himself. He didn’t hate the void per say, just some lingering annoyance from being trapped there. But he had to complain that jumping straight into the void wasn’t a good idea. Y/N reassures him that they got the okay from it, so it was fine. Gaster still wasn’t convinced, but went along with Y/N’s request anyways.

Descending through the void was weird and fascinating. Weightless yet Heavy, Falling yet Floating. An opening appeared right below them, drowning the area around the opening in bright light. The couple fell through, and their adventures may now begin.

Let’s see where they ended up first...

**Notes for the Chapter:**

> What is going to be the first one, i wonder? Well, let us take a peek!
> 
> (Living with his 'cousins' in a quite spacious modern 2 story house, this one will be 'falling' for you and will swoop you off of your feet! Smooth like butter and Precious like a gem, may we welcome our first Gent!)


	2. Feeling a little blue today, why is that?

**Summary for the Chapter:**

> The couple's first encounter with a Sans/Reader AU

**Notes for the Chapter:**

> Here ya go, this is the first of (probably) many!
> 
> Enjoy your skeleboi

Gaster and Y/N fell slowly onto the grassy ground, the void opening closing afterwards. It seems that they were in a forest, right by a park. Lucky break, they didn’t have to go through the forest to find civilization. Gaster apparently found it quite amusing if they were to be stranded and needed to find their way out. Que to Y/N jabbing Gaster on his side, warning him to not jinx the both of them.

The couple walked out of the forest and into the park, where there were, quite frankly, a lot of people and monsters. Nodding silently in agreement, the both of them went out of the park and walked down the sidewalk. The city was bustling with activity, honks of cars were heard, as well as the occasional screams of a Karen (*sighs* EVERY DANG TIME-).

Spotting an ice cream parlor in the distance, Y/N tugged Gaster’s arm. “Can we get ice cream?” They then pointed towards the parlor. “Of course, which one would you like?” Gaster asked, both already on the way to the shop. “I’m thinking, a scoop of dark chocolate and a scoop of crunchy salted caramel, if they have those” Y/N said, thinking whether to go for a cup or a cone. “A classic choice for you dear” Gaster snickered, because more often than not, Y/N’s choice of ice cream would either be that or a variation of it. 

On rare occasions, they’ll try something new. And a few skeletons back at home would latch onto that immediately, throwing their favorite (n)ice cream flavor towards Y/N to try.

“And what would you get G? Mocha or Toffee?” Y/N asked, knowing it’s either of those two options. Gaster would not order any other flavors unless it was given to him by Y/N, or he was in a particularly happy mood and was willing to try other things.

“I’m thinking more of an alcohol infused chocolate ice cream if they have it available to purchase” Gaster suddenly said, making Y/N stare at him in slight shock. “Oh wow, you’re trying something new today” They looked impressed. “What if this was just a ploy for me to drink in broad daylight, dear?” Gaster looked towards Y/N with a seemingly normal smile, hiding the cheekiness behind it. “Gaster, we both know that if you wanted to drink, you’d drink. Regardless of time and place” Y/N sighed, sadly that statement was true. If he really wanted, he could drink without anyone even batting an eye at him   
  
“ Touché my dear,  Touché ” Gaster chuckled at Y/N’s resignation, completely enjoying teasing his cute little partner. “Look, we’re here” He suddenly said, making Y/N look away from him and set their eyes on the ice cream parlor. Y/N found both of the flavors they wanted on display, and was now dragging Gaster inside the store. Fortunately, Gaster also found the ice cream he wanted, a little pricey considering the alcohol used in it, but it’s there nonetheless. Y/N speed-walked to the cashier and said their order, not even noticing the person beside them on the other cashier

**“A scoop of dark chocolate, and crunchy salted caramel with brownies on a cone please/thanks!”** Both people said at the same time, earning a look from the people manning the cashiers that thought this was staged or something. Y/N, a little shocked at the identical order, turned to face the other person just to see their own face staring back at them.  **“Eh!?”** Both Y/N’s cried out at the same time. Y/N wasn’t really surprised to see an AU of themself, but seeing them (AU Y/N) so soon was alarming. 

“I, uh, can explain this later. Uh, why don’t we just get our ice cream for now?” Y/N said to the other Y/N, who nodded dumbly. Gaster looked over and saw the scene, quickly saying his order and saying that he’ll cover the bill. Y/N said thanks and dragged (AU) Y/N out of the shop.

It seemed like fate was messing with our Y/N, as our first gent came running towards them, no doubt to check on the other Y/N. He was wearing a cream colored shirt with light gray pants and a classic black leather belt, and dark blue boots with 2 belts on each shoe of the same color, with gold buckles. A light blue bandana sat on his neck and he also wore matching light blue gloves. To top it all off, he wore a white jacket with a few Zigzag and stripes pattern in 2 primary colors, a turquoise green and dark blue (though not as dark or darker than his boots). He was also a skeleton, but that came as little to no surprise to our Y/N.

“Y/N, did you get your ice cream? And can you confirm i’m not hallucinating 2 Y/N’s?” Asked the skeleton, pointing at the two of them. “Look, uh, I can explain what happened, but can we please move to a more… quiet place?” Y/N said pleadingly towards the skeleton, who nodded. Gaster couldn’t have come out at a more fortunate time, catching them just before they left, ice cream in hand(s). Before anyone could ask anything, the skeleton began moving, the two Y/N’s following and Gaster not far behind.

The place they went to was certainly quiet, with little to no civilians in sight. The other Y/N snapped out of their daze along the way here, had been handed their ice cream, and was standing next to the skeleton. Our Y/N and Gaster stood right in front of the duo, Y/N ready to explain and Gaster ready to intervene if necessary

“So um, this might come as a surprise for you, uh Y/N, but i’m… you! From another universe..” Y/N said while laughing nervously, revealing their identity to the duo. They weren’t worried about the skeleton because chances are, he already knew about AU’s. No, what they were worried about was their counterpart. “My… Alternate… Self?” AU Y/N breathes out in disbelief, shock, and fascination. “Yeeess, that’s correct..” Y/N dragged out the ‘yes’ in nervousness   
  
“So Uh.. Blue.. alternate universes really exist?” AU Y/N asked the skeleton, who’s apparently named ‘Blue’. “Seeing as there’s proof standing right in front of us, it wouldn’t be so wise of me to lie, seeing as I am also an alternate self of someone” Blue stated. “So… The whole ‘cousin’ thing was a lie..?” AU Y/N asked slowly. “Technically we ARE connected in someway, but certainly not cousins” Blue lets out a nervous and conflicted puff of breath at the end of his sentence   
  
“Uh, weird question… Are the two of you dating?” Y/N asked with a flat, neutral tone. “Going strong for 3 months, other Y/N!” Blue answered for the both of them. “O-oh…” Y/N darted their eyes anywhere but the duo and finally settled on Gaster. They sent him a look, and Gaster spoke up, “I think it’s about time we took our leave. A pleasure to make your acquaintance, truly” He then proceeded to take Y/N’s hands and walked away. AU Y/N looked like they had so many more questions, but held back and watched as the couple retreated. The duo also went their merry way, still thinking about the encounter.

“That… was an interesting coincidence. Yeah… Interesting...” Y/N suddenly spoke up, finally starting to eat their ice cream. “You’re feeling a little guilty over the fact that your alternate self was dating an alternate version of my son” Gaster pointed out, eating his own ice cream that was put in a cup. They flinched, before caving in, “yeah, i guess you’re right…”

  
“I will admit, thinking of the possibility that if i didn’t find you, you would’ve ended up with my son of all people, makes me feel a little jealous” Gaster confessed what he was feeling at the moment, and it was all true. Gaster was jealous and was protective of you. If this were to continue, don’t be surprised if one of these visits, Gaster is just gonna stick by your side and never leave you be.   
  
“Oh look, there’s our ride” Y/N pointed at the tear that had appeared hidden in the corner where there was no one around. A black tendril came out of the tear and waved towards the couple. They went straight towards the tear, holding each other’s hands with their free arms. Still holding onto the ice creams, they walked/jumped into the tear that disappeared afterwards.

**Notes for the Chapter:**

> Aaaand that's a wrap for Bonely Hearts Club Blue!! Sorry if i didn't make the personality an exact match, i just didn't know how ;u;  
> But enough of that, let's see a glimpse of what's coming next!
> 
> (Where there's purity, there are always the tainted. These pair of brothers know exactly what those implies. Clubs had always been their second home, and an overdrive is not what they're looking for. Pole and lights, drinks and sweat, give it up for club roulette!)


	3. Purple and Cyan, Pink and Black. Is pole dancing really that hard?

**Summary for the Chapter:**

> Reader drank with Gaster and got dragged to dance with the brothers

**Notes for the Chapter:**

> ay yo, sup? Anyways-
> 
> Here is AU numero dos! (2)
> 
> yeah, i didn't think the whole thing through- sorry-

Rather than falling this time, it’s more like they emerged from the void tear on the ground. It was done in an alleyway, where no one was watching. It was better for the civilians this way rather than the couple, Y/N said so. Gaster suddenly stumbled, his senses were sensing something. “Ugh, Hormones…” Gaster mumbled, which Y/N heard. “I hear music, is it connected in some way?” asked Y/N. “Most likely a club, or something along those lines. The hormones are overwhelming, I don't think even all the monsters back in our universe could match up to this. A strip club maybe?” Gaster deducted from just those two points. They walked out of the alleyway to the sidewalk, only to be assaulted in bright neon light just seconds after.

Looks like Gaster was right, sort of. The whole district was filled with all kinds of things, from clubs to bars to love hotels. Gaster coughed and Y/N’s face grew a little red, but fanned it away pretty quickly. They were an adult, this was a normal occurrence. Looks like most of the civilians walking about are monsters, with a few humans mingling among the crowd. “Looks like it’s pretty crowded huh, Gaster?” said Y/N, already eyeing the district trying to find certain spots for various reasons. They are pretty cautious, thanks to Gaster probably.

“I suppose so,” Gaster hummed, analyzing their surroundings. “Since we’re already here, wanna go for a drink, G? It’s night time after all” Y/N grinned playfully, which Gaster returned with an amused chuckle. “I suppose we could, did you spot a bar somewhere?” Gaster inquired, being pulled along by Y/N not even a second later. They stopped at a certain place, and Gaster was gathering himself before looking up at the sign. It says Grillby’s <3~, with the heart. Gaster raised a bonebrow at Y/N

“It looked similar, so probability is high that Grillby’s managing this place” Y/N said to Gaster. It actually makes sense if you think about it, but why would Grillby’s put their location here? They suppose they should just go in and see for themselves. Gaster opened the door, and was hit directly with hormones. The inside was pretty much the same as regular Grillbys, except for the color scheme and the fact that there’s a pole in the corner of the room, right next to a jukebox. Guessed they moved those closer to the pole, for a reason which Gaster and Y/N figured out pretty quickly. Pole dancing.

They moved swiftly towards the bar stools, passing by a few patrons. Short booty shorts and crop tops were pretty much the trend in this bar apparently. Along with skin tight jeans and leather jackets, it’s… To be blunt, slutty. Everyone looked like they were on a sexual overdrive. Even Gaster was complaining about the hormone smacking him in the face when they sat down. It was weird, and Grillby was nowhere in sight.

After talking for a bit, someone came out of the back. Feeling the heat, both of them deducted that it was Grillby. Though, they were shocked and confused when Grillby came out. The tip of his flames on his head were blue, he was wearing black sunglasses, a fishnet crop top that clearly showed his chest, matching fishnet gloves, white jeans and blue sneakers. This Grillby walked to the bar, and stopped right in front of them.

“ooo, haven’t I seen you before~ What can I get for you~?” Grillby seems to be talking to the both of them. Learning from the previous experience, it seems that Grillby had indeed seen Y/N before, this AU’s equivalent of Y/N that is. “One of your strongest drinks, please” Gaster said, not surprising Y/N the slightest. They didn’t want to admit it, but Gaster can hold his liquor, maybe a little too well. “I’ll just take a middle ground for the alcoholic drinks” Said Y/N. Not too strong, not too weak. It’s not like Y/N can’t hold their drink, it’s just that they didn’t want to get intoxicated or drunk right off the bat.

Grillby immediately went to work, getting the liquor (both human and monster ones) and mixing them to make the beverage. “A volcan fire magma, and an étoile sea” Grillby pulled down his glasses and winked before handing them the drinks. The volcan one literally looked like lava, swirling around in the glass, while the étoile one looked like the deep sea with specks of sparkling little dots.

“So~ Where are those boneboys of yours?” Grillby inquired from Y/N. “Hmm?” Y/N hummed in questioning while sipping their drink. “sans and Papyrus, weren’t you with them? Or are you hooking up with their father now~?” Grillby questioned with a smirk while signalling towards Gaster. Y/N slightly choked on the drink, gulping the drink in their mouth down before putting the glass on the counter. “Hmm~ Didn’t think so. You’re up in an hour by the way” Grillby reminded Y/N

“h-huh? For what?” Y/N asked, maybe Grillby thought that they were this AU’s Y/N. “The show? You promised sans to help with it, although reluctantly. It’s in an hour at the Roulette, or did you forget about that also?” Grillby hummed, already thinking of a plan. “I’ll do sans a favor, come, i’ll take you there” Grillby beckoned the couple to follow him out. Gaster was eyeing Y/N to say no, that it was none of their business. But poor Gaster, he had bonded with a little troublemaker that can’t say no if it’s their business, even if it’s an alternate version of themselves.

Drink left on the counter, and Gaster springing up to follow behind, Y/N went along with Grillby to the ‘Roulette’ place.

And what do you know? He dropped the two of you off at a club called ‘The Roulette’. Seems like someone was already waiting for them, or rather, Y/N as you were suddenly pulled away from Gaster and into the back changing room. You were fitted into a body hugging outfit that shows a bit of skin but not too much that it’s uncomfortable to wear, and a 4 inch black platform boots. “Thank goodness you came early, didn’t know what we would’ve done if we didn’t take the measurements again” the lady doing your hair expressed their relief.

You were then escorted out, and were left at the back of the stage. Some people were approaching the backstage, and you pretended to be calm and fine. And the irony of the situation really. The people coming through the doors were sans and Papyrus, in less than subtle outfits. And they even had their ecto summoned, god this AU is gonna be the death of you.

“heey beautiful, ready for the show?” Lust said, while pecking your cheek. Oh, Gaster is not gonna like that. “Oh, uh yeah..” you said, trying to recall your short awkward but fun pole dance routine that you started back at home for fun. “Do not worry and just go with the flow! There’s no routine here. It’s a free for all for everyone!” Pink encouraged them, and that sentence alone made you mentally sigh with relief.

“oh, we’re up. good luck papyrus, babe” Lust sent a flying kiss your way and stepped up to the stage, you followed not long after. Finally in position, you were in front of the pole, on stage, and in front of a sea of monsters and humans. With a stomach filled with butterflies that you quickly suppressed, the music began playing.

Y/N had an awkward start, but then got swept up in the music and lingering alcohol. Their moves were even more impressive than Lust and Pink. Then the brothers took Y/N’s lead, synchronizing for a short time, but enough to make the crowd roar. Gaster was looking at Y/N in disapproval, but can’t get mad at them for having fun. The show ended and the crowd once again exploded in cheers, roars and claps.

They went backstage, and Y/N immediately ran towards the changing room before anyone could even say congratulations. Changing in speed only rivaling sonic, they got changed and ran out before anyone could grab hold of them. On the way out, they passed by this AU’s Y/N who looked shocked at the appearance of our Y/N, but brushed it off as they ran inside, probably thinking that they were already too late.

Our Y/N met up with Gaster in front of a nearby deserted corner. “I’m… so… sorry... Gaster-” you said while gasping for air, Gaster rubbing slow circles on your back. “It’s quite alright, I could see that you were having fun, and there is nothing wrong with that” Gaster gave you a smile, which then turned into a short lecture. “Though i would like for you to not just agree with anything-” and it went on and on, that you just tuned him out. Luckily for you, the void seemed to think the same, as it appeared right behind you and sucked the both of you in, cutting off Gaster's lecture, much to your (and the void’s (probable)) comfort.

Bonus:

Panting while catching their breath, Y/N knew they were already too late. Seeing sans and Papyrus in sight, they quickly moved to apologize. "Sans, Papyrus, i'm so-" But then, they were quickly cut off by Papyrus. "You were amazing Y/N! Who knew you could pole dance that magnificently!!" cheered Papyrus while pulling them into a hug and peppering kisses on their face with sans nodding to Papyrus's proclamation, to Y/N's confusion. "But, i just arrived..?" The statement, or rather rhetorical statement made sans raise a bone brow and Papyrus to frown slightly in thought while lowering Y/N down gently. 

"but then, who was it that danced with us?" asked sans. Then, Y/N remembered the person they passed by earlier. "ah! I remember passing by a person just now. They looked exactly like me, though they were wearing make up. They came running towards the exit" Y/N said with a humm. "so, what you're saying is that, a person that looked so much like you, fooled us and took your place on the stage?" sans asked Y/N, who just shrugged. "Probably. Though, they weren't doing any expression that took pleasure in taking my place, they were just hurrying out like someone was on their tail. I wonder why.." Y/N asked to no one in particular, while also thinking about the skeleton in the black coat that looked like sans and Papyrus's father.

**Notes for the Chapter:**

> And that's the end for the Underlust brothers! (like i said, i didn't think anything through)  
> Here's a secret: Gaster actually watches Y/N while they practice their pole dance, even though they thought nobody was watching.
> 
> Here's a sneak peek of the next chappie!
> 
> (With a sharp-toothed permanent smile, this one would grin with gold. Red is his favorite color, reminding him of his origins. And in his world, it's kill or BE killed. Proceed with caution, as spice and danger are quite the concoction)


	4. Blue is stop, and Red is go. Think of Determination

**Summary for the Chapter:**

> Y/N and Gaster got separated, and Red is such a softie for his Y/N

**Notes for the Chapter:**

> BWAH, I'M ALIVE
> 
> Here, have red skele and short af chapter

It’s either a mistake, or the void is currently still having a playful grudge on Gaster, but when they were put in the next AU, Y/N and Gaster were separated. Sure, the easy way out would be asking the void to take them back, but Y/N wasn’t that weak.

The atmosphere was… Unpleasant to say the least. You could practically feel the threatening aura surrounding the place. Y/N was currently in a forest, judging from the cold, it’s probably in snowdin. Which meant that they were underground, and that wasn’t a good thing if coupled with the alarming tone they were feeling.

“ey, y/n, sweetheart, where ‘re ya?” a gruff voice startled Y/N, especially since the voice were calling their name. And ‘sweetheart’? Where did that come from? “ah, ther’ ya are'' the voice said suddenly, sounding really close to them. A pair of hands snaking to Y/N’s waist in a hug promptly made Y/N let out a yelp.

“what ‘re ya doin’ in the forest? ‘s cold out here, and not really human safe, heh'' Y/N turned their head to see sans. Well, not sans but an alternate version of him, Red. “let’s get cha to the house, wher’ ya ain’t freezing'' not even a second later, Y/N felt a sudden shift, which they associated with shortcuts, happen.

Few moments later, they were put down on something plush, a couch? Highly likely. “hang on, i’ll make some tea for ya” says Red, before disappearing in the kitchen. “hey- uh, sans? Where’s… Gaster?” Y/N asked, trying to find info to where, whether hers or this world’s Gaster, is. “th’ old man ‘s at the lab, why ya ask?” Red replied from the kitchen.

“c-can we go meet him after this..?” Y/N asks cautiously, not knowing if Red and His Gaster were on good terms. “thought ya don’t like the old man? why the sudden visit?” Red inquired from Y/N, emerging from the kitchen holding 2 cups, each holding a serving of tea, and giving one to Y/N before sitting down on the couch too

“no reason…” Y/N said cryptically while sipping the provided tea. “eh, why not. was planning on going there anyways. c’mon” Red held out his hand for Y/N to take, which they did. The tea was taken along too, why waste a perfectly good tea? That’s just rude. A blink and they were there, the lab.

Or at least, the upper part. Gaster was in the True Lab, or better known as the lower part of the lab. Red could shortcut straight to the true lab, but.. “security reasons are ridiculous in this place” he complained as both Y/N and Red stepped into the elevator bringing them down.

It… was eerily quiet. Not like the quietness of no people being here, no, it was the quietness of something that had gone wrong. Both Red and Y/N felt that something was amiss, so they cautiously went to check, with Red leading of course.

“..really, how off-putting..” came a voice from the hallway, one which Y/N recognized instantly. Out of the shadows of the hallway, emerged 2 figures. Gaster, and the other Y/N. 

This Y/N, upon seeing red, walked a little faster towards him, and finally collapsed on red. “wh- the fu-” said a very flustered and concerned Red. “Your Gaster was trying to take their trait essence and use it for ‘research’ purposes. I would keep an eye on him if i were you” said Gaster, patting his hands together to get rid of the lasting shelf dust.

“so- yer not-” Red said as he turned his head towards Y/N. They just shook their head, while giving Red the mug back. “Better go home and tend to them fast, Red” Y/N gave him a smile, before he shortcutted back to his house.

“Soo…. What happened with Red’s Gaster?” Y/N asked, now beside Gaster. “Nothing for you to worry about. Shall we get going?” He asked, which Y/N nodded to. Gaster walked back to the room where he came from, with Y/N in tow. It.. was messy to say the least, with Red’s Gaster knocked out at the corner.

A rift was already there, how it formed, we don’t know. But not wanting to be here any longer, Y/N pulled Gaster along and went inside the rift without looking back.

**Notes for the Chapter:**

> not much exposure for Red and Co. but ¯\\_(ツ)_/¯
> 
> anyways, next!
> 
> (Stars, Nebula, and Galaxies. It's everywhere, stretching as far as the eye can see. As good as it is as a date spot, be very careful of the gravity around it. Our friendly skele suggests to wear gravitational boots before going out, for your own safety!)


End file.
